1. Field of the Invention
The present invention is directed to a rate tube measurement system for measuring fuel injected by a fuel injector.
2. Description of Related Art
The development of multi-pulse common rail injection systems in which fuel injectors are actuated to provide pilot and/or post injections as well as the primary injection has prompted the need for new, end-of-the-line, functional test equipment that can measure the fuel injected by the fuel injector. While positive displacement, piston type measurement systems are sufficiently accurate to measure the amount of fuel in the pilot and/or post injections as well as the primary injection in multi-pulse common rail injection systems, they are typically very complex and costly. Consequently, such positive displacement, piston type measurement systems, are not suitable for use in the manufacturing assembly line environment where numerous systems are required to test a significant number of fuel injectors.
Conventional rate tube measurement systems have the advantages of being more robust and providing a “true” rate shape. However, conventional rate tube measurement systems are not designed to measure fueling in multi-pulse common rail injection systems. In particular, conventional rate tube measurement systems are not adapted to measure the amount of fuel injected during pilot and/or post injections, as well as the primary injection.
SAE Paper 2001-01-0527 discloses a common-rail fuel injection rate measurement system consisting of a pressure chamber with pressure sensors, an amplifier box, an output processing unit, a data processing unit, and a volumetric flow-meter. The disclosed system also includes a back pressure sensor, a temperature sensor, a back pressure relief valve, and a discharge valve. However, the measurement system disclosed requires complex processing and filtering of the captured sensor output in order to derive information regarding the injection event such as fuel injection quantity, variation, and/or rate shape. Such filtering and complex processing is necessary to remove the noise in the acquired data caused by the fuel pressure pulses that are reflected within the disclosed system. However, development of such filters and methods for processing the acquired sensor output is expensive. In addition, such filtering and processing of the acquired sensor output can decrease the accuracy of the system since the quality of the filters and methods used to process the acquired sensor output can render the results inaccurate. Furthermore, because the system disclosed in the SAE Paper is designed for use in a laboratory environment where technicians can take their time in conducting the desired experiments, there are no provisions or features for expediting the measurement of the fuel injected by the fuel injector being tested.
Therefore, there exists an unfulfilled need for a measurement system for accurately measuring the amount of fuel injected by a fuel injector. There also exists an unfulfilled need for such a measurement system that provides accurate injection measurements, but reduces the filtering and processing requirements that are required for prior art systems. There further exists an unfulfilled need for such a measurement system that facilitates measurement of the fuel injection quantity, variation, and/or rate shape, which can be utilized in an manufacturing environment.